Candida albicans is the most common fungal pathogen of humans, causing a wide range of mucosal and life-threatening invasive diseases. The C. albicans cell wall is a major therapeutic and diagnostic target, and plays a pivotal role in infection. It is increasingly clear that C. albicans cell wall integrity involves diverse gene products whose functional conservation is limited. We have identified a core cell wall signaling module that regulates phosphoinositides (investigator), the PKCMAPK cell integrity pathway and the progression (but not establishment) of candidiasis. In parallel studies, we screened C. albicans mutant libraries to identify transcription factors, protein kinases and potential receptors that govern cell wall integrity, as measured by caspofungin susceptibility, and that may mediate core module inputs and outputs. Our objectives are to determine pathway and mechanistic relationships among core module components and other cell wall integrity regulators, and to define the specific roles of pathways in the progression of candidiasis after initial infection. In defining pathway and mechanistic relationships, we will employ a panel of assays that have proven useful in models like S. cerevisiae and are routinely performed in our labs. Cell wall integrity mutants will be assayed in the presence and absence of caspofungin for investigator levels and localization, cellular phenotypes, gene expression alterations, synthetic genetic interactions, phenotype rescue by overexpression, and phosphorylation of downstream targets. Phenotypic and genetic relationships will be verified by studies of protein localization, protein-protein and protein-investigator interactions. Having defined regulatory pathways, we will test key mutant strains for the ability to cause progressive candidiasis in mice. By using a competitive infection model (the cis/trans pathogenicity test), we will be able to assess the relative contributions to progressive candidiasis of the intrinsic survival characteristics of a mutant (cis effects) and the host immune response elicited by the mutant (trans). This project will provide new insights into mechanisms by which C. albicans mediates caspofungin resistance and pathogenesis, and may facilitate the future development of novel diagnostics and therapeutics that consider both pathogen and host response.